Week-6 Challenge: EV Drivetrain
AIM:- EV Drivetrain
OBJECTIVE:-
1)Which types of power converter circuits are employed in an electric and hybrid electric vehicle?
2) An Electric Vehicle's powertrain with a 72V battery pack is shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'.
The other parameters of the electric vehicle are given below,
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 Volt second
Chopper Switching frequency = 400Z
3) Induction motor vs DC brushless motor by Wally Rippel
OBJECTIVE:- 1 Which types of power converter circuits are employed in an electric and hybrid electric vehicle?
1 DC-DC Converter:-
`AC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels.
Due to the automotive constraints, the power converter structure has to be reliable, lightweight, small volume, with high efficiency, low electromagnetic interference, and low current/voltage ripple`
DC/DC converters topologies (Conventional step-up dc-dc converter, interleaved 4-channels step-up dc-dc converter with independent inductors, and Full-Bridge step-up dc-dc converter) is carried out.
2 AC-DC Converter:-
The simplest AC/DC converters comprise a transformer following the input filtering, which then passes onto a rectifier to produce DC.
In this case, rectification occurs after the transformer because transformers do not pass DC.
However, many AC/DC converters use more sophisticated, multi-stage conversion topologies as depicted in figure 1 due to the advantages of smaller transformer requirements and lower noise referred back to the mains power supply.
Rectifiers are implemented using semiconductor devices that conditionally conduct current in one direction only, like diodes.
More sophisticated semiconductor rectifiers include thyristors.
Silicon controlled rectifiers (SCR) and triode for alternating current (TRIAC) is analogous to a relay in that a small amount of voltage can control the flow of a larger voltage and current
3 DC-AC (Inverter) induction converter:-
A power inverter, or inverter, is a power circuit device or circuitry that changes direct current (DC) to alternate current(AC)
The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of “converters” which were originally large electromechanical devices converting AC to DC.
The input voltage output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry.
The inverter does not produce any power; the power is provided by the DC source.
A power inverter can be entirely electronic or maybe a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry.
OBJECTIVE:- 2.An Electric Vehicle's powertrain with a 72V battery pack is shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'.
GIVEN DATA:-
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 Volt second
Chopper Switching frequency= 400 Hz
The vehicle speed-torque characteristics are given by the below equation
What is EV steady-state speed if the duty cycle is 70%
The motor voltage can be calculated as VM = vb.d where vb is battery voltage and duty cycle.
VM = 72v.0.7 = 50.4v
Armature resistance
Ra = Va/Ia
Ra = 72v/400 = 0.18 ohms.
The torque-speed relationship is established by this equation
T = V.Kϕ/Ra - (Kϕ)^2.
/Ra
Where v is the battery or supply voltage
Kϕ is the motor constant
Ra is armature resistance
is the angular speed of the motor in rad/s
T is the motor torque
Substituting all the given data we end up with an equation for torque.
T = 50.4 .0.7/0.5 - 0.72^2./0.5 = 70.56-0.98.......equation
From the data given another equation for the torque is provided
Ttr = 24.7 + 0.0051^2 ....... equation2
By combining equation 1and2 we end up with a single equation
70.56 - 0.98 = 24.7+ 0.051^2
0.0051^2+ 0.98 - 45.86 = 0 equation
The equation represents a quadratic equation ax2 + bx + c = 0 where the root x is given by
(α, β) = [-b ± √(b2 – 4ac)]/2ac
x represents the angular speed and by substituting the constant we get the values for 38.82 rad/s and -230.98 rad/s
The steady-state angular speed of the motor there is 38.82
objective:-3Induction Versus DC Brushless Motors
DC Brushless Motors:-
With brushless machines, the rotor includes two or more permanent magnets that generate a DC magnetic field (as seen from the vantage point of the rotor).
In turn, this magnetic field enters the stator core (a core made up of thin, stacked laminations) and interacts with currents flowing within the windings to produce a torque interaction between the rotor and stator.
As the rotor rotates, it is necessary that the magnitude and polarity of the stator currents be continuously varied – and in just the right way - such that the torque remains constant and the conversion of electrical to mechanical energy is optimally efficient.
The device that provides this current control is called an inverter.
Without it, brushless motors are useless motors.
Induction Motors:-
An induction rotor has no magnets – just stacked steel laminations with buried peripheral conductors that form a “shorted structure.”
Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor.
In turn, the frequency of this magnetic field as “seen” by the rotor is equal to the difference between the applied electrical frequency and the rotational “frequency” of the rotor itself.
Accordingly, an induced voltage exists across the shorted structure that is proportionate to this speed difference between the rotor and electrical frequency.
In response to this voltage, currents are produced within the rotor conductors that are approximately proportionate to the voltage, hence the speed difference.
Finally, these currents interact with the original magnetic field to produce forces – a component of which is the desired rotor torque.